Well, episode 5 came out...
Spoiler:
As I suspected, there really wasn't anything to worry about. I actually guessed it pretty darn well. I was sure from the moment I saw that preview that Yui would be tricked into going to the park, and sure enough Inaba immediately guided Yui to "a place that would make her smile" and she didn't even wake up from her sad daze until she was inside the park. She also went on the Ferris Wheel because she felt bad about refusing even though she's afraid of heights. And all Inaba's moves up there did was make Yui realize that Hiyama had been upset because she kept holding her feelings back rather than relying on him, acting fine when she was anything but. Then Inaba pulls a really, really jerky move: he "borrows" Yui's anklet, ties it to a balloon and sends it off so that she would stop looking and remembering the sad things. Instead of moving her, it just got her to start screaming and racing after the balloon.
Ultimately, Yui didn't get the balloon, and wound up lost in a haunted house following a kid who'd caught it, and Hiyama raced in after her without paying. After guiding her out, Hiyama agrees with Inaba's words that being with him would probably make her cry again and she might be happy and free from such stress with Inaba, but he refuses to leave and swears that he'll always be the first one to come running whenever Yui's lost and troubled. Sure enough, as I thought, her feelings never truly wavered even when she thought that Inaba was a nice guy, and she tearfully tells Hiyama that he's the only one who can make her cry tears of joy or sadness with a single word. Later, the emotional moment makes them awkward to the point that people start to think they split, so she tries to get some alone time with him at the bathhouse, where she winds up discovering that he's been working to try and get his parents to buy him a cell phone, so that Yui would always be able to contact him in an instant if something happened. Finally, Hiyama repeats/reveals the wish he made on the anklet, wishing on a rainbow that he would be able to hurry and become the sort of grown up that could protect Yui properly.
Yet another good episode, and my assessment of Yui seemed to be pretty accurate: her feelings are strong enough that they won't sway so easily. She's just not really good at turning people down when she likes them, even platonically, which results in her easily getting put in situations that trouble her or look bad. Here's hoping she eventually manages to get over that habit. Even if she's mistaken and a boy doesn't have feelings for her, telling a male friend that she'd rather not be that close to someone besides her boyfriend is definitely better than leaving things vague and open to misinterpretation by all parties.